The present invention is directed generally to residential and small commercial HVAC systems, and more particularly to a low cost control assembly for such systems to control the delivery of forced air to various zones served by a single system which control assembly can be either heating priority responsive or cooling priority responsive.
Typical residences and small commercial buildings are often heated and cooled by a single forced air heating, ventilating, and air conditioning (HVAC) system. In the most basic system, a single thermostat generally placed at a convenient central location senses the temperature at that location and, based on that sensed temperature, can cause the HVAC system to supply heated air or cooled air to the closed structure. Often such closed structures exhibit temperature variations which can often amount to 6 to 8.degree. F., and can be even larger. In order to minimize the temperature variation from one region of the structure to another, various means have been employed to divide a structure into zones to be supplied by different amounts of heated or cooled air.
A very basic approach shown in U.S. Pat. No. 5,413,165, in which heated air from an upper level of a structure is directed to a lower level of a structure during the heating cycle to lessen the heating differentials between the upper and lower level. The flow of air into the individual zones can be manually controlled by switches in each zone as shown in U.S. Pat. No. 4,243,174, however, such a manual control system based on room occupancy fails to address the circumstances of large variations in temperature throughout a residence or small commercial building where all rooms are in use.
A very expensive solution is provided by U.S. Pat. No. 3,567,115 in which a pair of duct systems are created, one carrying hot air and the other carrying cold air, both sources of air being connected to each zone within the structure. While such a system might be satisfactory for certain large commercial situations, it is not generally thought to be economically feasible for residences and light commercial situations.
A number of systems have been developed for controlling the delivery of conditioned air from HVAC systems which employ a master thermostat and a first selected area or zone which is the principal control for the HVAC system. The master thermostat is then coupled to one or more slave thermostats, each of which merely controls a damper admitting air into one of the various zones. The zone controlled by the master unit can be either a permanent selection as disclosed in U.S. Pat. Nos. 4,931,948, 4,932,466, and 5,092,394, or can be subject to later modification through switches or jumpers in a control panel as disclosed in U.S. Pat. No. 4,830,095.
Fairly sophisticated zone controls employing highly programmable, solid state controls which permit a variable amount of air volume into each of the zones as shown in U.S. Pat. Nos. 4,997,029, 4,997,030, 4,754,919, 4,479,604, and 4,460,123. Such programmable systems tend to be fairly expensive at the time of initial purchase and are subject to rather catastrophic failure as a result of voltage or current spikes occurring through the power system due to lightning strikes or other electrical interference.
Accordingly, it is an object of the present invention to provide a low cost zone control system for controlling a HVAC system providing forced air into a single duct leading to a number of zones in which air is admitted past an open damper which may be closed by a control system incorporating a thermostat in each zone, each thermostat being of equal stature with regard to the system, the system being either heating priority responsive or cooling priority responsive.